This invention is concerned with a transfer printing process. More particularly, this invention is concerned with a transfer printing process of particular use in the preparation of security documents, such as passports and identity cards.
On identity cards, passports and the like there are generally at least two levels of printing, which may also include features which are not normally visible to the unaided eye. In this context, xe2x80x9cprintingxe2x80x9d is not limited to readable alphanumeric information, and includes any form of indicia which can be placed onto a surface of the document. The base sheet is often a so-called security paper, or may even be a synthetic paper-like sheet material other than paper, such a TESLIN (Trade Mark) sheet.
The first level of printing occurs when the base sheet for the document is prepared. This may involve background printing of, for example, a security pattern, the identity of the issuing agency, numerical data, a watermark, an encodable magnetic strip, and a holographic image. Further, some or all of this printed material may be applied to one or both sides of the base sheet.
The second level of printing occurs when personalised information identifying the person to whom the document is to be issued is applied to the base sheet. In the past this has usually involved text information, such as name, address, date of birth, a personal identification number, a document serial number, either of which may be in alphanumeric format or as a bar code, and date of issue. Although images of the holder have been used for many years in passports particularly, these have been in the form of a photograph as such, which has been attached in some way, usually by a gluing step, to the base sheet, which is often followed by a laminating step to protect the photographic image. In more recent practise, this pictorial information identifying the holder, such as a photograph or a fingerprint, is printed directly onto the base sheet, using computer based imaging systems.
Several techniques have been described both for preparing a base sheet carrying printed indicia at both levels, and for enhancing the inherent security of the resulting document. One example of this is the discontinuance of the use of a conventional photographic print which is attached in some way to the base sheet. Experience has shown that it is very difficult indeed to protect such a photograph adequately to prevent tampering with the document to alter it. However, although replacement of a photograph, and even all of the second level printing, by a computer generated image overcomes many of the recognised problems with the older methods of preparing security documents, it also has certain disadvantages. The chief problem is that in the printing techniques that have been used to date either a special printer is required, or an existing printer is significantly modified. In addition, a special printing technique is often used which has properties that are significantly different to the standard printing media, such as conventional printing ink and laser printer toners. One example of a special printing technique is the use of a laser which literally burns information into the document. Another example is described by Waller, in U.S. Pat. No. 5,890,742. In this process, the second level printing is applied directly onto a silicone coated surface of a transfer sheet. The printed release sheet is then positioned adjacent an adhesive layer on a security laminate, and transferred onto the adhesive layer. After removal of the transfer sheet, the security laminate is combined with a data receiving page carrying any desired first level printing. It can thus be seen that this is a complex process, which actually forms the second level printed image on the laminate, not the receiving page.
There is therefore a need for a document preparation process which both provides an acceptable level of security to the finished document, thus rendering it resistant to tampering and alteration, and which also only requires the use of standard printing equipment and printing techniques. Further, there is a need for such a process which additionally is able to print computer generated images including both pictorial information such as a photograph or fingerprint, and the more conventional alphanumeric information. This will allow the issuing authority to use current printing equipment meeting the standard requirements for document production with no more than a minimal level of adjustment.
Additionally, there is a need for a security document printing process which can be used to print material directly into a pre-prepared multi-page document, such as a passport, without using either a specially designed printer or any other special equipment. This need arises since conventional printing equipment uses single sheet (or roll) feed, and cannot print into a pre-prepared booklet, such as a passport. Although this difficulty can, to some extent, be avoided when the document is initially prepared, it cannot be avoided when additional information has to be added; a particular example is the addition of a printed visa to a passport.
This invention seeks to provide a process whereby the difficulties with the known process are effectively avoided. By the use of a transfer printing process, a printing process is provided which both uses conventional equipment, and which can be used to add second level printing to an existing document, especially a multi-page one such as a passport. With the process of this invention it is therefore possible to assemble the document, such as a passport, completely and to the highest security standards before any second level printing is included into it. Additionally, this printing process can readily be used to apply second level printing to both sides of the same base sheet. Further, in this process all of the printing equipment and materials used, particularly in producing the second level printed image, are standard commercially available equipment and materials requiring no modification.
In the process of this invention a multi-step procedure is used. Initially, all of the information to be applied in the second level printing procedure to the base sheet is assembled as a complete image, preferably using computer based imaging technology. The information can then be reviewed for both accuracy and completeness on a suitable screen. The image is then printed in reverse, as its mirror image, onto the silicone coated surface of a silicone release paper. The image can again be checked for accuracy and completeness. A conventional laser printer is used for this printing step. The release paper carrying the image and the base sheet are then placed into a heated press, with the image adjacent the base sheet. By the use of heat and pressure the image is transferred effectively completely from the silicone release surface onto the base sheet. After removal from the press, and allowing the document to cool, the release paper is removed, leaving the second level printed image on the base sheet.
Thus this invention seeks to provide a transfer printing process for applying an image to a document base sheet including the following steps:
(a) assembling the image;
(b) converting the image into its mirror image;
(c) printing the mirror image onto a silicone coated surface of a release substrate by means of a laser printer or photocopier to provide a stable toner particle copy of the mirror image;
(d) combining the release substrate and the base sheet, with the toner particle copy of the mirror image in contact with the base sheet;
(e) applying sufficient heat and pressure to the combined release substrate and the base sheet to transfer the toner mirror image onto the base sheet; and
(f) removing the release substrate to provide a base sheet carrying the image.
Preferably, both image preparation and conversion in step (a) into its mirror image are carried out within a computer imaging system.
Preferably, a laser prister is used in step (c).
Preferably, a twin platen single sheet press in used in step (d), having one unheated platen, and one heated platen, and the base sheet is located adjacent the unheated platen. More preferably, a twin platen single sheet press is used in step (d), having one unheated platen, and one platen constructed and arranged to be both heated and cooled, and the base sheet is located adjacent the unheated platen.
Conveniently, the base sheet comprises one sheet of an existing document. Most conveniently, the base sheet comprises a sheet within a passport or equivalent multi-page document. Alternatively, the base sheet comprises the inside face of the cover page of a multi-page document.
Conveniently, in order to obtain as constant an applied pressure over the whole surface of the base sheet, a layer of deformable material, such as an elastomeric layer or cardboard, is located in the press between the base sheet and the unheated platen.